1. Field of the Invention
The present invention relates to elastic wave devices including a film stack stacked on a support substrate.
2. Description of the Related Art
An elastic wave device disclosed in WO 2012/086639 A1 below includes a film stack located on a support substrate and a piezoelectric thin film stacked on the film stack. The film stack includes a high-acoustic-velocity film and a low-acoustic-velocity film. The low-acoustic-velocity film is a film along which a bulk wave propagates at a lower acoustic velocity than a bulk wave propagates along the piezoelectric thin film. The high-acoustic-velocity film is a film along which a bulk wave propagates at a higher acoustic velocity than an elastic wave propagates along the piezoelectric thin film.
An elastic wave device disclosed in WO 2009/104438 A1 below includes a piezoelectric thin film on which a support layer and a cover member define a hollow space. An IDT electrode is sealed in the hollow space.
The piezoelectric thin films of the elastic wave devices disclosed in WO 2012/086639 A1 and WO 2009/104438 A1 include piezoelectric single crystals, for example, LiTaO3. Such piezoelectric thin films are easily cracked and chipped due to external force. In particular, such piezoelectric thin films may be cracked and chipped when stress is applied, for example, during the step of bonding external connection terminals and dicing.
The elastic wave device disclosed in WO 2012/086639 A1 may also suffer interfacial delamination in the stack including the piezoelectric thin film during the attachment of external connection terminals and dicing.
For an elastic wave device as disclosed in WO 2009/104438 A1, it is necessary to maintain the sealed condition of the hollow structure. The sealed condition of the hollow structure is typically checked by leak detection, and accordingly the elastic wave device is screened out if the elastic wave device is defective. However, if the hollow structure as described above is applied to the stack disclosed in WO 2012/086639 A1, it may be impossible to check the sealed condition of the hollow structure by leak detection. In this case, it is difficult to screen out the elastic wave device by leak detection if the elastic wave device is defective.